To provide a stapler improved in designing flexibility of a main body cover covering a predetermined area of a clincher arm, by devising a mechanism for inhibiting rotation of a magazine.

The stapler is formed of: a magazine 9 provided with a pusher guide 21 for guiding a pusher 10 for pushing and energizing staples; a clincher arm 5 having a clincher 16 for bending legs of each staple driven out by a driver 13, and axially supporting rear ends of a driver arm 3 and the magazine 9 in a rotatable manner; and a rotation regulating mechanism 80 for regulating rotation of the magazine 9 between the magazine 9 and the clincher arm 5. The rotation regulating mechanism has a projection obtained by extending part of the pusher guide 21 downward from an opening formed in a bottom surface of the magazine 9, a hollow pin 47 having a length slightly shorter than an internal width of the clincher arm 5, and inserted into a bore formed in the projection, and protrusions 5f, 5g formed on inner surfaces of the clincher arm 5. The hollow pin 47 is abutted the protrusions 5f, 5g from below.